The cosmetics industry and the pharmaceutical industry very regularly use synthetic thickening polymers to increase the viscosity of creams, emulsions and various topical solutions. The synthetic thickening polymers currently used in these fields are provided in two physical forms, the powdered form and the liquid form for which the polymer is dispersed in an oil with the aid of surfactants and which is commonly called invert latex.
The most widely known thickening polymers in powdered form are the polymers based on acrylic acid and the copolymers based on acrylic acid and its esters. There may be mentioned for example the polymers marketed by the company Noveon under the trade name CARBOPOL™ and PEMULEN™. They are described in particular in American patents U.S. Pat. No. 5,373,044, U.S. Pat. No. 2,798,053 and in European patent EP 0 301 532.
In cosmetics, homopolymers or copolymers based on 2-acrylamido-2-methyl-propanesulphonic acid are also and always used in powdered form. These thickening polymers are marketed under the trade name Aristoflex™ and are described in particular in European patents EP 816 403, EP 1 116 733 and EP 1 069 142. These thickeners in powdered form are obtained by precipitation polymerization, which triggers numerous successive steps of purification of the final product in order to remove therefrom any trace of residual solvent.
Self-reversible invert latexes do not exhibit this disadvantage and are very rapidly dispersed in water. On the other hand, they contain a lot of oil and one or more surfactants which, in some cases, cause skin intolerance reactions. However, this problem has not yet been fully satisfactorily solved by the mere replacement of one oil by another. Furthermore, self-reversible invert latexes do not allow the preparation of clear gels.
The applicant has therefore searched for novel thickening systems which do not have the disadvantages mentioned above while having adequate thickening properties for them to be an acceptable alternative to the compositions of the state of the art.